New Clues Into Mystery of Mars Meteorites & Rocks Revealed

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Scientists are a step closer to reconciling a mystery on Mars, a
cosmic oddity centered on Martian rocks and pieces of the Red
Planet discovered on Earth.

The composition of meteorites long suspected to come from Mars
have confounded scientists for a long time. Planetary scientists
know that rocks sampled from the Martian surface are high in
nickel, yet the Martian meteorites (known as the SNC
meteorites ) happen to have significantly less nickel than
those other sampled rocks.

"The Spirit rover in the Gusev crater found nickel concentrations
five times as high in the crater than in the meteorites," Bernard
Wood, a geologist at the University of Oxford and lead author of
the study, said.

It's in the oxygen

Wood and his team found that oxygen is a key element that
could explain the chemical components of these rocks.

The older rocks sampled by the Spirit rover
(in operation on Mars until 2010) formed under more oxygen-rich
conditions, while the young meteorites were crafted in a
low-oxygen environment, according to Wood's model.

"[In Wood's model] the upper mantle of Mars was more oxidized
than the lower mantel, so when you partially melt the upper
mantle, you get these ancient rock compositions and when you
partially melt the less oxidized lower mantel, you get the
Martian meteorite compositions," said Hap McSween, a planetary
geologist at the University of Tennessee who is unaffiliated with
the study.

When the volcanic liquids that produced the SNC meteorites were
formed under low-oxygen conditions in Mars' interior, sulfides
remained behind as the liquids rose, leaving nickel trapped in
the deep interior. The volcanic rocks were therefore low in
nickel, Wood said.

The surface rocks, found in the Gusev crater, were formed in a
high-oxygen environment in Mars' interior where the sulfides —
together with their nickel — dissolved in the volcanic liquid.
The rocks are therefore nickel-rich.

A tectonic past?

The rocks in the Gusev crater formed more than 3.7 billion years
ago while the SNC meteorites date back 118 million to 1.3 billion
years, Wood said. This plays into the theories scientists have
about Mars' past.

"It's still consistent with one idea of
Mars, which is that it's sort of wet and warm … and the
atmosphere was oxidized very early on, that's certainly an idea
that's been kicking around for a long time," Wood told SPACE.com.

Wood applied his knowledge of Earth's geological processes to
understand what might be happening on Mars.

"On Earth, we know that we cycle oxygen rich rocks into the
Earth's interior through plate
tectonics, through so-called subduction," Wood said. "The
oxidized surface materials are pushed down into the interior and
so we argue that’s a plausible explanation for Mars."

Although that explanation could account for why the older but
oxygen-rich rocks were found in the upper mantle while the
oxygen-poor rocks came from a deeper part of Mars' interior,
McSween doesn't think there is necessarily evidence to support a
tectonic past on Mars.

"Although there are some suggestions that Mars might have had
plate tectonics at some point, there really is no evidence for
it, but this is at least a suggestion that something presumably
cycled oxidized materials from the surface back into the upper
mantle and maybe that's in the cards here," McSween told
SPACE.com.